add GIT_SHALLOW_FILE to propagate --shallow-file to subprocesses

This may be needed when a hook is run after a new shallow pack is
received, but .git/shallow is not settled yet. A temporary shallow
file to plug all loose ends should be used instead. GIT_SHALLOW_FILE
is overriden by --shallow-file.

--shallow-file does not work in this case because the hook may spawn
many git subprocesses and the launch commands do not have
--shallow-file as it's a recent addition.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

cache.h

@@ -354,6 +354,7 @@ static inline enum object_type object_type(unsigned int mode)
 #define DB_ENVIRONMENT "GIT_OBJECT_DIRECTORY"
 #define INDEX_ENVIRONMENT "GIT_INDEX_FILE"
 #define GRAFT_ENVIRONMENT "GIT_GRAFT_FILE"
+#define GIT_SHALLOW_FILE_ENVIRONMENT "GIT_SHALLOW_FILE"
 #define TEMPLATE_DIR_ENVIRONMENT "GIT_TEMPLATE_DIR"
 #define CONFIG_ENVIRONMENT "GIT_CONFIG"
 #define CONFIG_DATA_ENVIRONMENT "GIT_CONFIG_PARAMETERS"

commit.h

@@ -202,7 +202,7 @@ extern int is_repository_shallow(void);
 extern struct commit_list *get_shallow_commits(struct object_array *heads,
 		int depth, int shallow_flag, int not_shallow_flag);
 extern void check_shallow_file_for_update(void);
-extern void set_alternate_shallow_file(const char *path);
+extern void set_alternate_shallow_file(const char *path, int override);
 extern int write_shallow_commits(struct strbuf *out, int use_pack_protocol,
 				 const struct sha1_array *extra);
 extern void setup_alternate_shallow(struct lock_file *shallow_lock,

environment.c

@@ -10,6 +10,7 @@
 #include "cache.h"
 #include "refs.h"
 #include "fmt-merge-msg.h"
+#include "commit.h"
 
 int trust_executable_bit = 1;
 int trust_ctime = 1;
@@ -97,6 +98,7 @@ const char * const local_repo_env[] = {
 	INDEX_ENVIRONMENT,
 	NO_REPLACE_OBJECTS_ENVIRONMENT,
 	GIT_PREFIX_ENVIRONMENT,
+	GIT_SHALLOW_FILE_ENVIRONMENT,
 	NULL
 };
 
@@ -124,6 +126,7 @@ static char *expand_namespace(const char *raw_namespace)
 static void setup_git_env(void)
 {
 	const char *gitfile;
+	const char *shallow_file;
 
 	git_dir = getenv(GIT_DIR_ENVIRONMENT);
 	if (!git_dir)
@@ -147,6 +150,9 @@ static void setup_git_env(void)
 		read_replace_refs = 0;
 	namespace = expand_namespace(getenv(GIT_NAMESPACE_ENVIRONMENT));
 	namespace_len = strlen(namespace);
+	shallow_file = getenv(GIT_SHALLOW_FILE_ENVIRONMENT);
+	if (shallow_file)
+		set_alternate_shallow_file(shallow_file, 0);
 }
 
 int is_bare_repository(void)

git.c

@@ -162,7 +162,7 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
 		} else if (!strcmp(cmd, "--shallow-file")) {
 			(*argv)++;
 			(*argc)--;
-			set_alternate_shallow_file((*argv)[0]);
+			set_alternate_shallow_file((*argv)[0], 1);
 			if (envchanged)
 				*envchanged = 1;
 		} else if (!strcmp(cmd, "-C")) {

shallow.c

@@ -13,10 +13,12 @@ static int is_shallow = -1;
 static struct stat shallow_stat;
 static char *alternate_shallow_file;
 
-void set_alternate_shallow_file(const char *path)
+void set_alternate_shallow_file(const char *path, int override)
 {
 	if (is_shallow != -1)
 		die("BUG: is_repository_shallow must not be called before set_alternate_shallow_file");
+	if (alternate_shallow_file && !override)
+		return;
 	free(alternate_shallow_file);
 	alternate_shallow_file = path ? xstrdup(path) : NULL;
 }